1. Field of the Invention
This invention relates to an electrically conductive organic polymeric material and a process for its production. More specifically, it relates to an electrically semiconductive or conductive organic polymeric material useful as an electronics material having excellent oxidation resistance and mechanical strength, which is obtained by doping an insoluble and infusible substrate having a polyacene-type skeleton and composed of a heat-treated product of an aromatic polymer with an electron donating doping agent, or an electron accepting doping agent, or both, and to a process for producing the organic polymeric material.
2. Description of the Prior Art
Polymeric materials have excellent moldability, light weight, and mass-producibility. It has been desired therefore in the electronics industry and many other industrial fields to produce electrically semiconductive or conductive organic polymeric materials by utilizing these excellent properties. It is especially desired to produce organic polymeric semiconductors or conductors which have an electrical conductivity in the range of semiconductors or conductors, possess the properties of n-type or p-type semiconductors as in inorganic semiconductors such as silicon and germanium, and can be applied to diodes, transistors, solar cells, etc. by utilizing their p-n junction.
Early organic polymeric semiconductors or conductors were limited in application because they were difficult to mold into films or sheets and did not have the properties of n-type or p-type extrinsic semiconductors. Recent advances in technology have resulted in the production of organic polymeric materials having the properties of n-type or p-type semiconductors, which have relatively good moldability and can be formed into molded articles, and of which electrical conductivity can be greatly increased by doping them with an electron donating dopant or an electron accepting dopant. Polyacetylene and polyphenylene are known as examples of such organic polymeric materials.
For example, "Gosei Kinzoku" Kagaku Zokan ("Synthetic Metals" chemistry special issue) No. 87, pages 15 to 28, 1980 discloses that by polymerizing acetylene, polyacetylene (having an electrical conductivity of 10.sup.-9 to 10.sup.-5 ohm.sup.-1 cm.sup.-1) in film form is directly obtained, and by doping it with an electron donating dopant or an electron accepting dopant, an n-type or p-type semiconductor having a greatly increased electrical conductivity can be obtained. Polyacetylene, however, has the defect of being susceptible to oxidation by oxygen. For example, when polyacetylene is left to stand in air, it gradually absorbs oxygen and increases in weight, and with it, turns black brown and finally pale yellow. The rapidity of this oxidation reaction depends upon the crystallinity of polyacetylene. For example, even powdery polyacetylene having a relatively good crystallinity prepared with a Ti(O--n--C.sub.4 H.sub.9).sub.4 --Al(C.sub.2 H.sub.5).sub.3 catalyst system changes in composition to (CHO.sub.0.18).sub.x and drastically decreases in electrical conductivity when it is left to stand in air at room temperature for 2,000 hours. Thus, despite its excellent electrical conductivity, polyacetylene finds little practical application because of its poor oxidation stability.
Japanese Laid-Open Patent Publication No. 129443/1980 discloses that an n-type or p-type semiconductor having a greatly increased electrically conductivity can be produced by press-forming polyphenylene (an insulator having an electrical conductivity of about 10.sup.-12 ohm.sup.-1 cm.sup.-1) obtained by oxidative cationic polymerization of benzene, and doping the resulting molded articles of polyphenylene with an electron donating dopant or an electron accepting dopant. Unlike polyacetylene, polyphenylene has the advantage of possessing relatively good oxidation stability. Since, however, phenylene moieties are linked linearly by single bonds in polyphenylene, a conjugated system because carbon atoms is underdeveloped and there seems to be a limit in the level of its electrical conductivity which can be achieved by using a doping agent. Also, there seems to be a limit to the controllability of electrical properties by a doping agent. In fact, when polyphenylene is doped, for example, with halogen (an electron accepting dopant), the degree of its increase in electrical conductivity is smaller than that of polyacetylene doped with the same amount of halogen. Even when polyphenylene is doped with halogen in the largest dopable amount, its electrical conductivity does not increase beyond 10.sup.-7 ohm.sup.-1 cm.sup.-1 (see Example 5 of the above-cited Japanese patent document).